pub struct ClassName{
    field: i32,
}
impl ClassName {
    pub fn new(value: i32) -> ClassName {
        ClassName {
            field: value,
        }
    }
    pub fn public_method(&self){
        println!("from public method");
        self.private_method();
    }
    fn private_method(&self){
        println!("from private method");
    }
}